Alkylation Process Benzene Reduction Heavy Component Control
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Solution Overview
Problem
Current methods for reducing benzene content in gasoline, such as alkylation with light olefins, face challenges in meeting stringent benzene and residue (heavy hydrocarbon) regulations due to undesirable competing reactions like olefin oligomerization, which result in the formation of heavy components outside the gasoline boiling range.
Innovation Solution
Recycling an aliquot of the effluent from the alkylation reaction to maintain a sufficient molar ratio of alkylatable aromatic compounds to alkylating agent in the alkylation reaction zones, using a catalyst like MWW zeolites, ensures reduced benzene content and minimizes the formation of heavy components, thereby meeting regulatory standards without fractionation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If light olefins are used to alkylate benzene in gasoline to reduce benzene content, then benzene content is reduced, but heavy components are formed due to olefin oligomerization
Solution Approach 1:
The patent applies parameter changes by carefully controlling the aromatic to olefin molar ratio (maintaining at least 1:1), reaction temperature (30-100°C), and pressure (1-10 atm) to optimize the alkylation reaction conditions. These parameter adjustments favor benzene alkylation while suppressing olefin oligomerization, thereby reducing benzene content without excessive heavy component formation
Solution Approach 2:
The patent implements feedback control by continuously monitoring the benzene content in the gasoline stream and adjusting the olefin feed rate and reaction conditions accordingly. This closed-loop control ensures that benzene is effectively removed while maintaining optimal reaction conditions to minimize heavy component formation throughout the process
2Object-affected harmful factors
If stricter benzene regulations are enforced, then environmental compliance is improved, but meeting heavies level becomes increasingly difficult
Solution Approach 1:
The patent employs parameter changes by optimizing the aromatic to olefin molar ratio to at least 1:1, which ensures sufficient aromatics are available to react with olefins, preventing olefin oligomerization that would produce heavy components. This stoichiometric control allows the process to meet both stringent benzene specifications and heavies limits simultaneously
Solution Approach 2:
The patent applies preliminary action by pre-mixing the olefin feed with the gasoline stream containing aromatics before entering the reaction zone, ensuring proper mixing and immediate reaction. This preliminary preparation prevents olefin accumulation and subsequent oligomerization, allowing compliance with both benzene and heavies regulations
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The process effectively reduces benzene content to less than 0.62 volume % and limits heavy components to less than 2 volume % at atmospheric pressure, meeting both benzene and residue specifications simultaneously, without the need for fractionation of the reactor effluent.
Implementation Method 1
contacting a benzene-containing gasoline blend stock with a C2 to C4 olefin stream in the presence of a catalyst containing the zeolite, SSZ-25
Implementation Method 2
alkylation of reformate at low temperature over the zeolite catalyst, MCM-49
Data Source
AI summary
In a process for alkylating benzene contained in a benzene-containing refinery gasoline stream, the benzene-containing refinery gasoline stream is contacted with an alkylating agent selected from one or more C2 to C5 olefins in at least one alkylation reaction zone under alkylation conditions to produce an alkylated effluent which has reduced benzene content as compared with said refinery gasoline stream and is essentially free of said alkylating agent. An aliquot of the alkylated effluent is then recycled to the one at least one alkylation reaction zone such that the molar ratio of alkylatable aromatic compounds to said alkylating agent in the combined refinery gasoline and recycle streams introduced into the at least one alkylation reaction zone is at least 1.0:1.